This invention pertains to stress-crack resistant polyarylates and more particularly to bisphenol A iso/terephthalates modified with 4,4'-biphenol.
Polyarylates or polyesters derived from bisphenol A and iso/terephthalic acids are tough materials having a continuous use temperature of about 140.degree. C. However, as with many other amorphous thermoplastics, they possess poor solvent and stress-crack resistance. Such polyesters may be represented as having repeating units as shown below: ##STR1##
On the other hand, H. G. Weyland et al. reported in Euro. Poly J. 6, 1339 (1970) that a 4,4'-biphenol iso/terephthalate prepared by interfacial polymerization was both insoluble and infusible.
Isophthalates of 4,4'-biphenol modified with hydroquinone are described in U.S. Pat. Nos. 3,036,991 and 3,160,602. These copolymers contain at least 40 mol percent of hydroquinone isophthalate and were prepared via the reaction of the di-functional phenols with isophthaloyl chloride in solvents boiling above 300.degree. C. These polyesters are highly crystalline having melting points ranging from 350.degree. to 400.degree. C. Slowly cooled moldings are crystalline and translucent while rapidly cooled or quenched moldings are amorphous and transparent. No mechanical data are revealed in these references.
Linear co-polyesters have been prepared from terephthalic or isophthalic acid, a bisphenol and hydroquinone containing 5 to 35 mol percent of the hydroquinone.
Bisphenol A polyesters of isophthalic acid, terephthalic acid or iso/terephthalic acid mixtures lack solvent and stress-crack resistance.
4,4'-Biphenol polyesters of iso/terephthalic acid mixtures are solvent resistant but are not melt processable.
U.S. Pat. No. 3,939,117 discloses a method for producing a polyarylene ester at temperatures of 0.degree. to 100.degree. C. in an organic solvent for the polyarylene ester in the presence of solid Ca(OH).sub.2 and a polymerization catalyst. One or more divalent phenols and aromatic dicarboxylic chlorides are used but there is no appreciation of the use of a particular ratio of particular divalent phenols to afford polyarylates having enhanced solvent and stress crack resistance.